The present invention relates to the manufacture of modules containing a plurality of polymeric hollow fibers, for use in gas separation, air dehydration, or for other purposes. Specifically, the present invention provides a method and apparatus for automatically lacing bundles of such fibers, while the fibers are transported through equipment for manufacturing the modules.
It has been known to use a polymeric membrane to separate air into components. Various polymers have the property that they allow different gases to flow through, or permeate, the membrane, at different rates. A polymer used in air separation, for example, will pass oxygen and nitrogen at different rates. The gas that preferentially flows through the membrane wall is called the “permeate” gas, and the gas that tends not to flow through the membrane is called the “non-permeate” gas. The selectivity of the membrane is a measure of the degree to which the membrane allows one component, but not the other, to pass through.
A membrane-based gas separation system has the inherent advantage that the system does not require the transportation, storage, and handling of cryogenic liquids. Also, a membrane system requires relatively little energy. The membrane itself has no moving parts; the only moving part in the overall membrane system is usually the compressor which provides the gas to be fed to the membrane.
A gas separation membrane unit is typically provided in the form of a module containing a large number of small, hollow fibers made of the selected polymeric membrane material. The module is generally cylindrical, and terminates in a pair of tubesheets which anchor the hollow fibers. The tubesheets are impervious to gas. The fibers are mounted so as to extend through the tubesheets, so that gas flowing through the interior of the fibers (known in the art as the bore side) can effectively bypass the tubesheets. But gas flowing in the region external to the fibers (known as the shell side) cannot pass through the tubesheets.
In operation, a gas is introduced into a membrane module, the gas being directed to flow through the bore side of the fibers. One component of the gas permeates through the fiber walls, and emerges on the shell side of the fibers, while the other, non-permeate, component tends to flow straight through the bores of the fibers. The non-permeate component comprises a product stream that emerges from the bore sides of the fibers at the outlet end of the module.
One method for processing the fibers is described in U.S. Pat. No. 5,598,874, the disclosure of which is incorporated by reference herein. In the cited patent, the fibers are woven into a web, using a loom. After drying, the web is gathered into a rolled fabric mat which becomes the essential component of the module.
A serious problem with the above-described process is the tendency of the fibers to splay out while being automatically fed to the loom, and/or while being formed into a module. This splaying causes the fibers to become tangled, resulting in a ragged product. In some cases, the tangling can clog the feeder, and can require that the loom be stopped. Such stoppages obviously increase the overall cost of forming the fibers into modules. Also, it has been found that fiber modules having an excessive proportion of ragged fibers perform relatively poorly.
The present invention provides an automated system for reducing or eliminating the splaying of fibers, during the manufacture of a fiber membrane module. The invention not only reduces the effective cost of producing a module, but it also results in modules having improved selectivity.